1. Field of the Invention
This invention relates to a rolling guide unit for guiding the sliding of a tubular member along a rail.
2. Description of the Related Art
FIGS. 9 to 16 show an example of a conventionally known type of rolling guide unit. For example, Japanese unexamined patent publication 2001-082469 (FIG. 7) discloses such a type.
The conventional rolling guide unit is used for linearly guiding a member or transferring torque in a machine tool or an industrial machine, for example. Principal members of the rolling guide unit are a rail 1 secured to the machine and a cylindrical member 2 through which the rail 1 passes.
As shown in the sectional view of FIG. 10 taken along the A-A line in FIG. 9, the cylindrical member 2 includes a body 3, a pair of spacers 4 which are provided at the front and back in the sliding direction, a pair of end caps 5 which are respectively fixed with the spacers 4 interposed, and a pair of end seals 6 which respectively cover the outsides of the end caps 5. The spacers 4, the end caps 5 and the end seals 6 are secured to the body 3 with screws 7 as shown in FIG. 11.
FIG. 12 is a sectional view taken along the B-B line in FIG. 10 and showing a pair of raceway grooves 8 formed in the inner periphery of the body 3 in the axis direction. On the other hand, a pair of raceway grooves 9 are formed in the outer periphery of the rail 1 in the axis direction. As shown in FIG. 12, when the raceway grooves 9 of the rail 1 passing through the body 3 face the respective raceway grooves 8, the raceway grooves 9 and the raceway grooves 8 are correspondingly combined together to form a pair of raceway paths a.
The body 3 has a pair of through holes 10 extending in the axis direction. Sleeve-shaped oiled members 11 in cylindrical form and containing lubricating oil are inserted into the respective through holes 10. The interiors of the sleeve-shaped oiled members 11 are defined as a pair of return paths b.
The function of the sleeve-shaped oiled members 11 will be described in detail later.
As shown in FIG. 12, the body 3 has a pair of tapped holes 12 and a pair of positioning recesses 13 formed therein. Internal threads are respectively formed on the inner peripheries of the tapped holes 12. The screws 7 are engaged with the internal threads. The positioning recesses 13 are holes providing for insertion of projections p (see FIG. 15) formed on each of the end caps 5.
FIG. 13 is a sectional view taken along the C-C line in FIG. 10, and also a plan view of the spacer 4 when viewed from the corresponding end cap 5. As shown in FIG. 13, the spacers 4 each have raceway-path recesses 14 opening onto their inner peripheries, return-path holes 15, screw holes 16a and positioning holes 17 formed therein.
When the spacers 4 are mounted to the body 3, the raceway-path recesses 14 are respectively interconnected with the raceway paths a provided in the body 3 as shown in FIG. 10, and the return-path holes 15 are respectively interconnected with the return paths b provided in the body 3 as shown in FIG. 16. Further, the screw holes 16a are respectively interconnected with the tapped holes 12 provided in the body 3 as shown in FIG. 12. The positioning holes 17 are respectively interconnected with the positioning recesses 13 provided in the body 3.
Each of the end caps 5 is mounted on the spacer 4 as described earlier. As shown in the plan view in FIG. 14 of the end cap 5 when viewed from the body 3, each of the end caps 5 has direction-changing recesses 18 and screw holes 16b formed therein. When each of the end caps 5 is installed on the spacer 4, each of the direction-changing recesses 18 is interconnected with both the raceway-path recess 14 and the return-path hole 15 which are formed in the spacer 4 as shown in FIG. 13. This results in the interconnection between the raceway paths a and the return paths b by way of the direction-changing recesses 18.
Thus, the direction-changing recesses 18 formed in the end caps 5, the return-path holes 15 formed in the spacers 4, and the return paths b formed in the body 3 constitute two circuit paths each interconnecting the two ends of the raceway path a.
Such interconnections between the ends of the raceway paths a constitute a pair of endless paths. A plurality of rolling elements 19 such as balls are installed in the endless paths. The rolling elements 19 are placed in contact with a pair of the raceway grooves 9 in the rail 1 and a pair of the raceway grooves 8 in the cylinder 2 to produce a rolling motion so as to maintain the smooth motion of the cylinder 2 relative to the rail 1.
When the cylinder 2 is moved relatively to the rail in this manner, the rolling elements 19 in each of the raceway paths a circulate around the endless path passing through one of the direction-changing recesses 18, the return path b and the other direction-changing recess 18.
In the foregoing structure, for the over-term maintenance of a high-accuracy motion of the cylinder 2 relative to the rail 1, it is necessary to decrease the rolling resistance of the rolling elements 19, minimize the abrasion of the rolling elements 19 themselves, and minimize the abrasion of the raceway paths a and the return paths b along which the rolling elements 19 produce a rolling motion. For this purpose, there is a necessity to periodically or continuously supply lubricating oil to the rolling elements 19, the raceway paths a and the like.
Therefore, the aforementioned conventional rolling guide unit has the lubricating-oil-containing sleeve-shaped oiled members 11 installed in the through holes 10 in the axis direction in order to maintain the optimum lubrication. That is, each of the sleeve-shaped oiled members 11 is formed of a sintered resin material of a porous structure capable of including lubricating oil.
The rolling elements 19 roll in the sleeve-shaped oiled members 11, whereby the lubricating oil contained in the sleeve-shaped oiled members 11 appropriately seeps out onto the surfaces of the rolling elements 19. The rolling elements 19 receiving a supply of the lubricating oil thus seeping hereon roll in the raceway paths a and the return paths b so as to provide a supply of the lubricating oil to the overall path.
As well as the foregoing rolling guide unit disclosed in Japanese unexamined patent publication 2001-082469 (FIG. 7), the rolling guide unit disclosed in registered utility model 3066116 (FIGS. 12 to 14) is conventionally known.
The rolling guide unit disclosed in registered utility model 3066116 (FIGS. 12 to 14) has grease-including fabric protruding in the portions involved in the processes of the connection from the direction-changing recesses 18 to the through holes 10 in Japanese unexamined patent publication 2001-082469 (FIG. 7). Thereby, the rolling elements passing through the return path come into contact with the slightly protruding fabric containing grease, and receive a supply of the grease in the fabric.
The rolling guide unit disclosed in Japanese unexamined patent publication 2001-082469 (FIG. 7) has the sleeve-shaped oiled members 11 inserted into the through holes 10 in order to supply the lubricating oil to the rolling elements 19. However, a large inner diameter of each through hole 10 is required for the insertion of the sleeve-shaped oiled member 11. In other words, the required inner diameter of each sleeve-shaped oiled member 11 is equal to or larger than the diameter of the rolling element 19.
Further, the thickness of each sleeve-shaped oiled member 11 depends on the amount of lubricating oil contained in this sleeve-shaped oiled member 11. Hence, the necessary outer diameter of each sleeve-shaped oiled member 11 is, at the minimum, equal to or more than the diameter of the rolling element 19 plus double the thickness of each sleeve-shaped oiled member 11. The reason for the addition of the double thickness of each sleeve-shaped oiled member 11 is because the sleeve-shaped oiled member 11 is formed in a cylindrical form.
On the other hand, when the sleeve-shaped oiled member 11 is not installed in the through hole 10, the required inner diameter of each through hole 10 is only slightly larger than the diameter of the rolling element 19.
In other words, in the case of installing the sleeve-shaped oiled members 11 in the through holes 10, it is necessary to increase the inner diameter of each through hole 10 by at least an amount corresponding to twice the thickness of each sleeve-shaped oiled member 11.
However, as shown in FIG. 12, the through holes 10 are formed within the thickness of the cylindrical-shaped body 3. Hence, the increase in the inner diameter of each through hole 10 means a decrease in the wall thickness of the body 3. The decreased wall thickness causes a lack of strength, and in some cases a hole may possibly be made in the side face. Therefore, when the sleeve-shaped oiled members 11 are installed in the body 3, the body 3 must be increased in outer diameter or decreased in inner diameter.
However, if the outer diameter of the body 3 is increased, the cylindrical member 2 is increased in size. If the inner diameter of the body 3 is decreased, the diameter of the rail 1 must be decreased, leading to a lack of strength in the rail 1.
In short, because the conventional rolling guide unit has structural limitations, the problem of a low degree of flexibility in design arises when the sleeve-shaped oiled members 11 are installed in the body 3.
Further, the rolling guide unit disclosed in registered utility model 3066116 (FIGS. 12 to 14) has the fabric projecting, just slightly, into the moving trajectory of the rolling elements. The smooth movement of the rolling elements may be impaired due to variations in sliding resistance to the rolling elements in the contact area between the fabric and the rolling elements.